In the human elbow, three degrees of freedom are present. These are flexion-extension, varus-valgus carrying angle and axial rotation.
The various elbow prosthesis available in the marketplace today have been constructed as a replacement for the natural human elbow. The two basic types of elbow prosthesis known in the prior art are semi-constrained and unconstrained. In semi-constrained prosthesis, the prosthetic joint is held together mechanically, by components of the prosthesis. Whereas in an unconstrained device, the prosthetic device is held together by the patient's natural soft tissues.
In each of these devices, one portion of the prosthesis is implanted in the humerus of the patient and the other portion is implanted in the ulna. The two portions then mate in some manner to allow articulation of the joint. Importantly, absent from the marketplace is a device that can be implanted when either the humerus or ulna and/or both bones are compromised either from disease or injury.
Prosthetic elbows currently marketed typically can be implanted to operate in one of two ways. These two ways are an unconstrained or unlinked manner and the other way is a semi-constrained or linked manner. Unconstrained prosthetic elbows are more generally indicated for osteoarthritic or post traumatic patients with strong soft tissues about the elbow.
Typically, unconstrained elbows are designed with, for example, a metal humeral articulating surface and a polyethylene ulnar articulating surface. Each of these components having matching convex and concave surfaces, respectively.
The semi-constrained prosthesis is usually used in patients that are suffering from an inflammatory disease. The inflammatory disease results in the patient having weaker soft tissue and significant bone erosion. The weaker soft tissue and bone erosion makes the use of an unconstrained elbow more difficult in that the soft tissues are not of sufficient strength to properly contain the prosthetic components in contact with each other. A semi-constrained prosthesis typically uses a linkage pin at the elbow axis of rotation. Most commercially available elbow devices make use of a locking axis pin as the main element of articulation for the semi-constrained form of the elbow prosthesis.
A long standing need has existed for the orthopedic surgeon to have available an elbow prosthesis that addresses the clinical problems that result from a post-traumatic injury to the elbow. More specifically, currently no elbow implant designs exist that are specifically indicated for use to treat complex fractures of the distal humerus and/or proximal ulna.
Please note that for the purposes of this disclosure, the terms “prosthesis,” “implant” and “device” may be used interchangeably and have the same meaning herein.